1. Field of the Invention
The present invention relates to the field of power electronics. In particular, it relates to a gate turn-off power semiconductor component, comprising
(a) in a semiconductor substrate between an anode and a cathode a plurality of unit cells which are arranged next to one another and connected in parallel;
(b) in each of the unit cells, a thyristor structure with a sequence of alternatingly doped layers which comprises an emitter zone connected to a cathode contact, a first base layer, a second base layer which is common to all unit cells and an emitter layer connected to an anode contact; and
(c) for each emitter zone a field-effect controlled short-circuit which, together with the thyristor structure, forms an MOS-controlled thyristor MCT.
Such a component is known, for example, from the article by V. A. K. Temple, IEEE Trans. Electron Devices, Vol. ED-33, pp. 1609-1618 (1986).
2. Discussion of Background
For some years, the development of MOS-controlled components has been increasingly driven forward in power electronics. This trend was started by the unipolar power MOSFETs with DMOS structure (FIG. 1).
The main advantage of these MOS-controlled components is based on the high input impedance at the gate electrode. It enables the component to be driven with a comparatively very low power expenditure.
However, the DMOSFETs have an important disadvantage: because of the unipolar nature of conduction in these components, high breakdown voltages must be obtained at the cost of high forward resistances which limit the maximum current intensity.
To solve this problem, MOS-controlled bipolar structures have been proposed which combine the advantages of low-power MOS drive with the advantages of low-resistance bipolar current transfer.
One of these structures is known from the prior art as IGBT (Insulated Gate Bipolar Transistor).
Another structure which has been described in the article by V. A. K. Temple initially mentioned is the so-called MOS-controlled thyristor MCT (MOS Controlled Thyristor). Such an MCT, which consists of a plurality of adjacently located parallel-connected unit cells, is turned off by short circuiting the cathode-side emitter zones by means of an integrated MOSFET (FIG. 2).
Although the currently known bipolar MCTs are superior to the unipolar DMOSFETs in most fields for the abovementioned reasons, they still have the following disadvantage:
Every conventional DMOSFET has a parasitic diode structure 11 (drawn in FIG. 1) which is polarized in the reverse direction during normal operation (positive voltage at anode A).
It is generally known that in the case of inductive loads, the actual switch must be protected against the energy stored in the inductance during the switching process. In the conventional art, this is ensured by so-called antiparallel free-wheeling diodes within the circuit. Naturally, these additional components make a convertor, for example, more complicated and more expensive.
A new generation of power MOSFETs has recently become available in which the structure-inherent inverse diode described has been improved technologically to such an extent that it can also fully handle large inductive reverse currents. Discrete protective diodes can therefore largely be omitted in these modern MOSFETs.
However, this is not the case in the known MCTs.